Method and means for foundry practice



Patented Aug. 23, 1938 PATENT OFFICE METHOD AND MEANS FOR FOUNDRY rnac'rrca Charles Marshall Saeger, Jr., Bowmanstown, Pa.

No Drawing.

Application January 12, 1929, Serial No. 332,225

c Claims. (01. 22-188) lemma IllldGl' the act of March a, 1883, as

amended April 30, 1928: 3'10 0. G. 751) My invention relates to a new and .useful method of making molds and cores for metal Previously in this art the hot metal coming in 5 contact with the mold and core surfaces causes the sand in contact to burn into the adjacent surfaces of the metal and produces castings of rough exterior and interior surfaces, which surfaces are formed of an integral film of mixed in metal and sand. This, as well as the removal of the cores and the cleaning of the un-integral sand from the casting, has heretofore been an expensive, laborious and dusty task frequently requiring the use of pneumatic chisels and other tools, while in the machiningof such castings the integral fllm of sand and metal. is diflicult to machine unless the tool in its first cut penetrates beyondthe depth of such film.

In the prior art manycracked castings have been produced due to hard cores and molds which do not crush readily as the metal casting cools, contracts and solidifies, and such castings are a constant source of substantial loss in all foundries but more especially in aluminum and kindred metal castings.

A further constant source of substantial loss in the prior art of metal casting has resulted from mold and core blows due to the low permeability of the sand forming such molds and cores.

to In the past many endeavors have been made to overcome these very objectionable conditions and losses. Some of these attempts have been to form the molds and cores of green sand, which is the ordinary molding sand of commerce, but the as liability of such molds and cores to be washed in part into the molten flowing metal being cast prevents, or renders hazardous, their use in many cases.

To provide molds and cores of more strength 40 than possessed by green said molds and cores, it heretofore has been common practice to embody a binder in the sand of, either or all, clay, molasses and water, flour and water, and oil, and to indurate such molds and cores by baking. Such molds and cores have all the aforesaid defects except the tendency to wash into the flowing molten metal, while the thus formed harder molds and cores increase the cracking liability of the castings as well as tend to increase the liability of the castings to blow'du to the lesser porosity of such molds and cores.

In the prior art water has been employed as a diiutent of the active binding material employed but its surface tension, rate of evaporation and other conditions, are such that it requires substantial labor in order to properly mix the same .with the constituent material of the mold or core,

while its vaporizing point is so high as to leave much of the water in the mold or core or requires that such mold or core be baked sufliciently to 5 remove such moisture, which baking to the degree required to remove such moisture produces a hard core or mold with its said liabilities.

In the overcoming of the aforesaid conditions and losses I have devised a method of producing 10 molds and cores for metal castings which contemplates the addition to the sand forming such molds and cores, either or both; rubber or a rubber-like substance in solution ordispersion which may be mixed throughout the whole mass of such 15 molds and cores or the surface of the mold or core or both that comes in contact with the metal to be cast may be impregnated with such rubber or rubber-like substance in solution or dispersion. The solution being formed by any desirable sol- 20 vent of rubber or rubber-like material, or said dispersion being formed by small particles thereof in a liquid, and such solvent or liquid is prefers ably of the class that may readily be evaporated so that a further step in my method, that of dry 25 ing the mold or core may readily be accomplished either by atmospheric temperature or by moderate heat as the eiement of time or other production factors may determine to be most economic or desirable. when the molds, and such cores as 30 they may have, are thus dried the molten metal may be cast therein and the heat of such cast metal in contact with the surfaces of the molds,

as well as of such cores that they may contain,

causes the rubber or rubber-like binder to be destroyed by said application of said heat. Said destruction, disintegration or the loss of its binding efllciency, does not take place until a predetermined'time, after the molten metal has been poured in the mold and/or about the core, said 40 4 time being after the process of solidification of the cast metal, or at least the surfacesthereof juxtaposed to the mold and/or core, has rendered such metal, or said surfaces thereof, not fluid, otherwise the casting would be liable to be rendered defective or useless by the particles of the mold and/or core, which are by the heat of said casting no longer bound together, being washed into or becoming commingled or imbedded in the casting. In the said application of said heat to the exposed sin-faces of the mold,

' and core or cores that the mold may contain, the

presence of-rubber or rubber-like material causes the surfaces of the metal not to burn in or inter- 55 mingle with substantially any of the sand as it does in the prior art.

As to this last named phenomenon, applicant has not yet been able to learn the agencies which produce this end. He has with his associates accounted for said phenomenon on two theories either or both of which may explain the existence of said phenomenon.

One of said theories is that the hot surface 01 the casting in contact with the rubber impregnated sand mold and core forms a gaseous layer adjacent to the hot metal surfaces which prevents the sand adhering to or being embedded .into the hot metalsurfaces.

The other theory being that such hot metal in contact with such rubber-like impregnated sand results in the formation of free carbon which coats the grains of sand and thereby prevents such coated sands from either directly coming in contact with or being embedded in the surface of the casting.

It has further been found that the grains of sand forming the mold and the cores that have been impregnated or mixed with said rubber or rubber-like material are, due to the heat of the casting, coated with decomposition products of rubber occasioned by the conversion of said rubber or rubber-like material, and this condition is believed to be the main or contributing factor in rendering especially the cores to be most readily removed from all castings; whereas in the prior art it has been the usual custom of requiring as much as a day for the removal of some cores from a single casting with the best labor saving appliances.

In order to demonstrate the practical utility of my said method I have caused many molds and cores to be constructed in accordance with my said method and in so constructing the same I have formed a rubber or rubber-like solution embodying for instance "1 lb. of rubber or rubber-like substance dissolved in 2 gallons of gasoline and have therewith moistened or tempered the dry sand to the usual or required molding consistency. From such moistened or tempered sand I have caused the molds and cores to be formed. Then I have dried such molds and their required cores, if any, either by atmospheric temperature or by the application of moderate heat thereto according to convenience or the production speed required. When dried the casting may be made in the assembled mold with the cores therein that may be required.

Under favorable conditions where the strength I of the ordinary green sand mold or core would be 2.4 lbs. per square inch, my said method of producing a mold or core results, for instance, in the same having a corresponding strength of 10.8 lbs. per square inch and yet the permea-' bility of my sand molds and cores is as great as, if not greater than, the green sand molds and cores so that practically from the blowing of either molds or cores. However, I have, by my said method or process, produced molds and cores at atmospheric temperatures of greater strength than baked molds and cores, but when subjected to the casting ,heat they are or greater gas premeability and yieldsbility, to casting shrinkage, by employing, different proportions of solvent and rubber or rubber-like material, or less of the elastic and more of the plastic properties of such materials.

In the old art where great difllculty has always been experienced in removing cores from castings, some of which have to be virtually chipped no castings are lost.

out a piece at a time, my method wherein the heat destroys the binder, renders the cores granular and free flowing as dry sand. In the old art where clay and other binders were used which when burnt by making one casting could notbe used with molding sand to form the exterior surfaces of the mold, with my method, in removing the casting from the mold the core sands will shake out of the core holes and mingle with the exterior surface molding sands which, with my method, is unobjectionable because even any core sands may be reused while in the prior art core sand that has been previously used in mak- I objectionable in usual production due to their has been present in the substantially higher rate of evaporation as their employment renders diiiicult the even distribution of such solvents with their rubber content throughout the sand unless such sand be mixed therewith under conditions in excess of atmospherlc pressure or with greater than normal rapidity.

While it has been stated that the rubber or rubber-like substance or material has been reduced to the form of a solution before the sand is applied to or commingled with the material forming the mold or core, yet this is only one of the convenient ways for obtaining such a mixture. Another of such ways being that the rubber or rubber-like material or substance is reduced to a granular or powdered form and directly mixed in such condition with the sands or other material forming the mold or core. The interlocking characteristics of such a mixture in practice may aflord the requisite bond, but in such cases where the shape or weight or other characteristics of the mold or core may not be thus afforded the requisite bonding capacity, such capacity may be substantially increased by the application to the mass of a moderate degree of heat and pressure, either or both.

A further beneficial accomplishment of my invention is that it enables castings to be produced without oxidized surfaces so that the bright unoxidized surfaces of the cast metal appear when removed from the mold. This produces a casting of better appearance and tends substantially to deter subsequent oxidizing tendencies. This is more especially advantageous in producing castings of the more readily oxidizable metals as well as with such castings having relatively thin portions which are not required to be finished. Furthermore, such molds and their cores, and the heat action of the molten metal thereon tend to avoid any harmful action upon the casting and its surface that may be set up in the other than rubber or rubber-like material content of the mold and core.

In the binders of the prior art with which water molds or cores or has been employed as a diluent, it is the theory that, when the hot metal is cast into or against molds or cores bonded with such binder, the heat of the thus causes contact of said oxidized surfaces of the cast metal with the uncoated or uninsulated sand grains, and which results in the fusing, imbedding into or adherence of said sand to the surfaces of the casting. This action also leaves a substantial oxygen content, residual from the air,

in the casting-cavity of the mold, which is being filled with the hot liquid metal, and which oxygen also promotes oxidation of the metal surfaces and the removal of said char from the mold or core surfaces, thus contributing to said fusing of and adherence to the casting surfaces.

In the binder which I employ with a diluent whose volatility is substantially greater than water, and-which contains substantially less oxygen, the theory is that when the hot metal is cast into or against molds or cores bonded with such binder, the heat of the liquid metal vaporizes said diluent relatively more rapidly and quickly forms a gas or vapor which expels or replaces the air content of the cavity of such mold, and which gas or vapor thus formed is in itself more free from oxygen than water vapor. These conditions, namely, the occupation of said cavity by a reducing or non-oxidizing gas or vapor, promote the charring of the binder upon the mold or core surfaces, tend to prevent the removal of such charred coating by oxidation or combustion, and thus preclude the fusion or adherence of the mold or core particles with or to the surfaces of the casting.

Upon said conditions in the prior art, and in my invention, the prior art castings are formed in the presence of an oxidizing gas or vapor, while in my invention the castings are formed in the presence of a non-oxidizing gas or vapor.

The active constituent which I employ as a binder should, I have discovered, he sparingly present in the parts of the mold or core at, or close to, the surface of the hot casting and should be prevented from collecting or accumulating at or near any such surface, as, under the aforesaid theory of the action of my invention, said active constituent upon the casting-surface of the mold or core is of such low charring temperature that it may char before the cast metal fills the mold, whereby the lighter of the thus combusted gases may escape from the mold which is ventilated by the usual poring and riser grates until the casting-cavity of the mold becomes full of cast metal. Such char is only required tobe thin to prevent the material forming the mold and core from being imbedded in, or adhering to, or fusing with the surface of the casting. The constituent material of the mold or core requires but little of said active constituent of my binder to bind said material. Thus, in respect to ob taining said surface char as well as said binding economy in the use of said active constituent is not only desirable but is in many cases productive of the best results. The presence in the mold at the time of the casting therein, of the nonoxidizing gas or vapor tends to prevent the removal of such char and promotes said economy,

since the sparing amount of char-producing substance upon such surfaces that is originally placed there remains to prevent the fusion of the mold or core particles with the surfaces of the casting.

In order to economically attain said results, I

the substantial absence of air and dilute or weaken the normal strength of said active constituent by admixture with another substance, all ingredients of such mixture being preferably either in powdered or liquid form before or after such admixture.

In order to obtain the most economical results in a liquid form of said active constituent a liquid diluent is employed whose surface tension is substantially less, and whose rate of evaporation is substantially higher, and whose other qualities are substantially more favorable than those of water. For instance, when a drop of water is placed on an impervious surface, force is required to spread said drop over said surface due, in part, to the high surface tension of water; but when a fluid of substantially lesser surface tension is, for instance, dropped upon such a substance, such fluid more readily spreads over a wide area of such surface. While capillary action has some tendency of decelerate such spread over a pervious surface of the same substance, the problem in an economical core binderis to have thebinding fluid quickly spread over the external surface of the particles of the substance to be bonded together, as the fluid absorbed by capillary action into the pores of such particles is substantially wasted from a binder sense.

- Thus, I have discovered, that the requisite dilu a tion of the active constituent of my binder :bya

fluid of substantially lower surface tension, andwhose rate of evaporation is substantiallyhigher,

and whose other qualities are more favorable,=

from the molds and cores, even by air drying,

before castings are formed therewith.

In this specification and its appended claims where the term, rubber, is employed it is intended to include rubber either as latex, coagulated rubber, or sap from trees such as Hevea braziliensis, or from vines or shrubs, as well as from other kindred vegetation such as guayule containing more or less rubber hydrocarbon. The

rubber may be unvulcanized or consist of vulcanized soft rubber, and may have been previously subjected to an elevated temperature.

By rubber-like material employed in the specification and its appended claims it is desired to be understood as referring to any substance, either or both plastic and elastic, that have any of the substantial characteristics of rubber, balata or gutta percha, and may include old rubber'scrap that has been treated either at an elevated temperature alone or otherwise. It may also include any rubber or scrap rubber, either or both, that has been subjected to an elevated temperature alone or in the presence of sulphuric acid or a sulphonic acid or a sulphonyl halide or-it may also include a substance such as is an article of. commerce under the name Thermoprene".

.than ,those of water also greatly facilitates the Serial No. 332,226, filed January 12, 1929, for Process and product for coating molds cores", and Serial No. 429,227, filed February 17, 1930, for Method and means for foundry practice.

Having now so fully described my invention that others skilled in the art may therefrom make and use the same, what I claim and desire to secureby Letters Patent is:

1. In the method of producing cores and molds, the step of mixing with component material oi. such molds and cores rubber in divided particles adapted to be combusted by the heat of the casting.

2. In the method of producing cores and molds, the step of mixing with the material for the entire body of such molds and cores rubber in solution.

3. The method of making a core for metal castings consisting in mixing a quantity of sand with a binder including a thermoprene cement of the G. P. type, forming a core from such mixand stance is to be sn ture, and permitting the core to cure in contact with the air. f g 4. A core material i'or sand cores comprising an aggregate and a solution of a thermoprene oi the gutta-percha type as a binder. 5. A core binder for foundry refractory substances comprising a solvent, volatile at room temperatures, containing an adhesive rubber compound having the physical characteristic oi disintegrating into granular carbon within the range of temperature to which the refractory sub- :lected during the cooling of the cast metal.

6. A casting mold or core for metal casting comprising a granular refractory substance bound together throughout with an adhesive rubber compound having the physical characteristic of disintegrating into granular carbon within the range of temperatures to which the mold or core is to be subjected during the cooling oi. the cast 20 metal.

CHARLES MARSHALL SAEGER, Ja. 

